A company's AI ethics policy requires that AI systems affecting individuals must be contestable. In practice, what does effective contestability require?

B is correct because contestability requires a functioning pipeline: individuals must know a decision was made by AI, receive a meaningful explanation of the basis, and have access to an actual review process where challenges are considered and can change outcomes — not merely a nominal complaints channel. A is overbroad — not every challenge must result in reversal. C confuses contestability with the right to rectification. D is an architecture constraint that is not required for contestability.